Showing papers on "Optical communication published in 1992"

Fiber-Optic Communication Systems

Abstract: Preface. 1 Introduction. 1.1 Historical Perspective. 1.2 Basic Concepts. 1.3 Optical Communication Systems. 1.4 Lightwave System Components. Problems. References. 2 Optical Fibers. 2.1 Geometrical-Optics Description. 2.2 Wave Propagation. 2.3 Dispersion in Single-Mode Fibers. 2.4 Dispersion-Induced Limitations. 2.5 Fiber Losses. 2.6 Nonlinear Optical Effects. 2.7 Fiber Design and Fabrication. Problems. References. 3 Optical Transmitters. 3.1 Semiconductor Laser Physics. 3.2 Single-Mode Semiconductor Lasers. 3.3 Laser Characteristics. 3.4 Optical Signal Generation. 3.5 Light-Emitting Diodes. 3.6 Transmitter Design. Problems. References. 4 Optical Receivers. 4.1 Basic Concepts. 4.2 Common Photodetectors. 4.3 Receiver Design. 4.4 Receiver Noise. 4.5 Coherent Detection. 4.6 Receiver Sensitivity. 4.7 Sensitivity Degradation. 4.8 Receiver Performance. Problems. References. 5 Lightwave Systems. 5.1 System Architectures. 5.2 Design Guidelines. 5.3 Long-Haul Systems. 5.4 Sources of Power Penalty. 5.5 Forward Error Correction. 5.6 Computer-Aided Design. Problems. References. 6 Multichannel Systems. 6.1 WDM Lightwave Systems. 6.2 WDM Components. 6.3 System Performance Issues. 6.4 Time-Division Multiplexing. 6.5 Subcarrier Multiplexing. 6.6 Code-Division Multiplexing. Problems. References. 7 Loss Management. 7.1 Compensation of Fiber Losses. 7.2 Erbium-Doped Fiber Amplifiers. 7.3 Raman Amplifiers. 7.4 Optical Signal-To-Noise Ratio. 7.5 Electrical Signal-To-Noise Ratio. 7.6 Receiver Sensitivity and Q Factor. 7.7 Role of Dispersive and Nonlinear Effects. 7.8 Periodically Amplified Lightwave Systems. Problems. References. 8 Dispersion Management. 8.1 Dispersion Problem and Its Solution. 8.2 Dispersion-Compensating Fibers. 8.3 Fiber Bragg Gratings. 8.4 Dispersion-Equalizing Filters. 8.5 Optical Phase Conjugation. 8.6 Channels at High Bit Rates. 8.7 Electronic Dispersion Compensation. Problems. References. 9 Control of Nonlinear Effects. 9.1 Impact of Fiber Nonlinearity. 9.2 Solitons in Optical Fibers. 9.3 Dispersion-Managed Solitons. 9.4 Pseudo-linear Lightwave Systems. 9.5 Control of Intrachannel Nonlinear Effects. Problems. References. 10 Advanced Lightwave Systems. 10.1 Advanced Modulation Formats. 10.2 Demodulation Schemes. 10.3 Shot Noise and Bit-Error Rate. 10.4 Sensitivity Degradation Mechanisms. 10.5 Impact of Nonlinear Effects. 10.6 Recent Progress. 10.7 Ultimate Channel Capacity. Problems. References. 11 Optical Signal Processing. 11.1 Nonlinear Techniques and Devices. 11.2 All-Optical Flip-Flops. 11.3 Wavelength Converters. 11.4 Ultrafast Optical Switching. 11.5 Optical Regenerators. Problems. References. A System of Units. B Acronyms. C General Formula for Pulse Broadening. D Software Package.

Optical Signal Processing

Abstract: : We studied optical processing techniques to detect and track frequency hopped radio signals in a dense electromagnetic environment by using cross-spectrum of two signals obtained from antenna elements spaced by one-half an RF wavelength. We decimate the array by retaining only every Mth element and scan the cross-spectrum past the decimated array. We therefore reduce the circuit complexity, but suffer some loss in system performance because we require more photodetector bandwidth to accommodate the scanning action. An extension of the decimated array concept is to decimate the reference waveform in the heterodyne spectrum analyzer. In this case, we generate only 64 optical probes in the Fourier domain instead of the 2048 that are normally required. The advantage is that all of the optical power in the reference beam can be concentrated into the reduced number of optical probes, thereby offsetting some of the intrinsic loss in performance experienced by the cross-spectrum analyzer. (JHD)

Small signal analysis for dispersive optical fiber communication systems

Abstract: A small signal analysis for analyzing the conversion between intensity and phase modulation or noise in a dispersive fiber is given. Using this theory the small signal response of laser diodes with respect to intensity and phase modulation in dispersive optical fibers is derived. Guidelines are also given for considerably reducing the intensity noise if a fiber with a suitable dispersion is used. All analytical calculations are compared with numerical simulations and good agreement is achieved. >

High performance optical wavelength shifter

Abstract: A broadband (>50 nm) wavelength shifter capable of switching multigigabit data between optical frequencies in the 1.5 μm region is presented. The device, based on gain saturation in a semiconductor optical amplifier, is tunable, has gain, and is nearly polarisation insensitive. Data degradation after wavelength shifting is negligible.

All-optical clock recovery using a mode-locked laser

Abstract: A novel all-optical clock recovery scheme in which an optical data stream is used to mode-lock a fibre laser at (or an integer multiple of) the line rate is experimentally demonstrated. A length of data transmission fibre is shared with the fibre laser and mode locking occurs through the process of crossphase modulation.

Wavelength division multiple access channel hypercube processor interconnection

Abstract: A hypercube-based structure in which optical multiple access channels span the dimensional axes is introduced. This severely reduces the required degree, since only one I/O port is required per dimension. However, good performance is maintained through the high-capacity characteristics of optical communication. The reduction in degree is shown to have significant system complexity implications. Four star-coupled configurations are studied as the basis for the optical multiple access channels, three of which exhibit the optical self-routing characteristic. A performance analysis shows that through the integration of agile sources or receivers, and wavelength division multiple access, systems can be developed with significant increases in performance yet at a reduction in communication subsystem complexity. >

Fiber grating-based sensing system with interferometric wavelength-shift detection

Abstract: A system for sensing a measurand field, the system comprising a source of broadband light, a sensor, an unbalanced optical interferometric apparatus, and a signal processor. The sensor produces an optical return signal having a wavelength functionally dependent on the measurand field. The interferometric apparatus produces an electrical interference output signal having a phase shift functionally dependent on the wavelength of the return signal, and the processor develops a processing signal indicative of the measurand field value.

Efficient optical communication in parallel computers

Abstract: We study the problem of interprocessor communication in a parallel computer model suggested by recent advances in optical technology. The units of the computer (processors with local memory) communicate with each other by transmitting messages. A processor can transmit a message to any other processor, and transmission takes constant time. If two or more processors try to send a message to the same processor no transmission is successful and retransmission must occur. We show how to implement an extremely simple and efficient form of randomized routing in this model. We study, in particular, the problem of realizing arbitrary h-relations. In an h-relation, each processor is the source as well as the destination of at most h messages. We propose a simple and practical distributed randomized algorithm for realizing arbitrary h-relations on an n-processor such network within O(h + log n log log n) parallel communication steps. Our algorithm is pure in the sense that no information aside from actual messages is transmitted between processors. Anderson and Miller [1] and Valiant [19] have derived a @(h + log n) algorithm for the same problem, which achieves optimality for a slightly larger range of h. Their algorithm is complicated as opposed to ours that we believe to be practical. Optimal interprocessor communication algorithms in realistic models of parallel computers are not only interesting in their own sake, they are one of the main components in optimally simulating PRAMs as well aa implementing Valiant's bulk-synchronous parallel model [13, 19, 18]. 1 Introduction Optics has been used in the design of special purpose computing devices for quite some time now, especially in the field of signal processing. Recent technological advances make it also an appealing alternative to electronics in the design of general purpose computers. The use of optics has been suggested in such diverse areas as storage, processing, and for providing communica-t put of this ~e~e=ch wss done ~hile the second author WVM Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice k given that copying is by permission of the Association for Computing Machinery. To copy otherwise , or to republish, requires a fee andlor specific permission. tion between different modules within computer systems. The use of optical interconnects …

Erbium-doped fiber amplifiers

Abstract: Erbium-doped fiber amplifiers (EDFA’s) operate in the 1.5?m wavelength telecommunications window and have achieved high gain, high output power and near ideal noise performance. The feasibility of using semiconductor laser diodes to pump EDFA’s insures that EDFA’s are practical devices which will have great impact on optical communications as power boosters, optical repeaters and optical preamplifiers.

Performance analysis of direct-detection optical CDMA communication systems with avalanche photodiodes

Abstract: Direct-detection optical code-division multiple-access (CDMA) communication systems with avalanche photodiode (APD) photodetectors are investigated. A Chernoff upper bound, modified Chernoff upper bound, and Gaussian approximation on the probability of bit error are presented for general APDs and arbitrary

Generation and control of microwave signals by optical techniques

Abstract: Optical techniques for microwave signal generation and optical control of microwave devices are described. Optical generation of microwave signals to 35 GHz and above by coherent heterodyne was carried out by FM sideband injection locking of laser diodes and by offset frequency phase locking of solid state lasers. Applications of optically generated microwave signals including optical control of phased array radar and photodetector characterisation are discussed. Optical injection locking, phase control, and phase locking of microwave oscillators are also presented.

Optical polarization division multiplexing at 4 Gb/s

Abstract: An optical polarization multiplexing system using BPSK coherent heterodyne detection to transmit 4 Gb/s over a 45-km standard single-mode fiber optical link at a receiver sensitivity of -35 dBm is described. The 4-Gb/s system has a potential receiver sensitivity of -40 dBm while using 2-Gb/s baseband electronics. >

Ultrafast polarisation-independent all-optical switching using a polarisation diversity scheme in the nonlinear optical loop mirror

Abstract: Polarisation-independent 32 to 8 Gbit/s demultiplexing in the nonlinear optical loop mirror is successfully demonstrated using a novel polarisation diversity scheme in which two independent switching operations are performed along the two principal axes of a polarisation-maintaining fibre loop. The variation of the switched signal powers is measured to be less than 1 dB as the input polarisation direction is varied over 180°.

Intensity modulated digital optical communications using a frequency modulated signal laser

Abstract: In long distance digital and frequency modulation systems that use optical sources having optical frequency chirp, degradation due to optical dispersion in the transmission fiber is overcome by filtering the laser wavelength representative of one of the binary levels (e.g., binary "0"). An optical source such as a DFB laser is directly frequency modulated by a digital data stream. A first digital level is represented by a first intensity of the modulated carrier corresponding to a carrier wavelength λ1 and a second digital level is represented by a second intensity of the modulated carrier corresponding to a carrier wavelength λ2. A wavelength selective reflector is used to filter the wavelength λ1 from the modulated carrier. The modulated carrier, from which wavelength λ1 has been filtered, is then coupled to an optical communication path for transmission. In one embodiment the wavelength selective reflector is coupled to the laser output using an optical circulator. In another embodiment, a directional coupler is used.

Optical signal channel selector

Abstract: The optical signal channel selector apparatus includes one or more first optical channels, and a plurality of a secondary optical channels for carrying an optical signal. A parabolic mirror is rotatable to provide optical communication between a first optical channel and any one of the secondary optical channels. A position encoded stepper motor is coupled to the parabolic mirror for controlling the position of the mirror. Solid state optical interface blocks having one or more filters receive the optical signal and transmit output optical signals with filtered wavelength ranges in the secondary optical channels. The rotation of the mirror by a position encoded stepper motor allows selection of a desired secondary channel, and automatically shutters the remaining channels closed.

Optical communications systems for the subscriber area with optical amplifiers

Abstract: Optical communications system for the subscriber area with optical amplifiers. The system according to the in-vention is used to distribute information signals, particularly telephone signals, from a center to a large number of subscribers and to make possible a bidirectional transmission of telephone and data signals between the center and the subscribers. According to the invention, the network used for this purpose is a multistar fiber-optic network in which fiber-optic amplifiers (10, 11) are present between successive branch points. The information signals to be distributed are transmitted via the fiber-optic network with a first wavelength (.lambda.1) to the sub-scribers, and the subscriber-specific information signals to be transmitted from the center (1) to the subscribers (Ti) are converted by frequency modulation to a different frequency band (FB2) than the distribution signals (by frequency modulation) and transmitted to the subscribers at the same wavelengths as the distribution signals, and the subscriber-specific signals to be transmitted from the subscribers (Ti) to the center (1) are converted by frequency modulation to another frequency band (FB3) and are transmitted optically to the center with a second wavelength (.lambda.2). This optical signal is amplified at suitable points (A) and several alternative embodiments for this amplifi-cation are indicated.

Railway coded track circuit apparatus and method utilizing fiber optic sensing

Abstract: A railway track circuit system utilizing an optical sensor which emits a vehicle detection light signal when a railway vehicle is present in a track section. A reference light signal is also generated by a light emission source. A detector in optical communication with the optical sensor receives the vehicle detection light signal. Information contained in the vehicle detection light signal is interpreted by a processor to detect the railway vehicle. In presently preferred embodiments, the sensor may comprise an elongated optical fiber conductor extending along the track section or a plurality of cascaded localized sensors. The sensor may generally also be utilized as a communication medium to pass communication data between opposite ends of the track section. Depending on the exigencies of the particular application, the sensor may be located within the track section in a number of ways.

Optical interconnects using top-surface-emitting microlasers and planar optics.

Abstract: Optical interconnections made using two-dimensional arrays of top-surface-emitting microlasers and integrated free-space optics are discussed for use in chip-to-chip communications. A demonstration setup with a 2 × 2 array of lasers is presented. System parameters, such as light efficiency, the number of data channels, thermal effects, power requirements, and the issue of hybrid integration of laser chips with passive optics, are considered.

Optical communication equipment and optical communication method

Abstract: An optical communication terminal detects an unused first wavelength in a wavelength range in response to a transmission request and transmits a call signal to a transmission destination using the first wavelength. An acknowledgement signal from the destination is detected in a portion of the wavelength range not including the first wavelength. When a call signal addressed to the terminal from another terminal is detected thereat and the terminal is ready for communication, an unused second wavelength in the wavelength range is detected and an acknowledgement signal is sent using the second wavelength in response to the call signal.

Optical communication system using coplanar light modulators

Abstract: An optical communications system includes apparatus for interferometric signaling in which light signals are propagated from a first location so as to form at least one predetermined interference pattern at a second location remote from the first location and then the received light signals are demodulated at the second location. The apparatus includes a substantially coherent light source and a plurality of adjacent, substantially coplanar optical modulators in the path of the emitted light.

Optical interconnects based on arrays of surface-emitting lasers and lenslets

Abstract: A compact free-space optical system that uses arrays of surface-emitting lasers and lenslets for chip-to-chip and board-to-board optical communication is described. A seven-channel optical interconnect has been demonstrated at 300 Mbits/s per channel, and we describe how such a system can be expanded to several hundred channels while its compactness and alignability are retained.

Distortion compensation for analog optical systems

Abstract: A distortion arrangement for analog optical communication systems is disclosed which is capable of compensating for system-level distortion attributable to a number of factors including, but not limited to, frequency-dependent transmitting device characteristics, transmission fiber dispersion, doped fiber amplifier gain variations. The distortion arrangement includes a distortion signal path (36) which is configured to characterize the total system nonlinearity, utilizing for example a harmonic generator (38), derivative generator (48), attenuating means (adjustable) (44,50) and time delay means (adjustable) (46,52). The distortion arrangement may be co-located with an optical transmitter and defined as a predistortion arrangement or, conversely, co-located with an optical receiver and defined as a postdistortion arrangement. In general, both a predistorter and postdistorter may be utilized.

Suppression of stimulated Brillouin scattering using optical isolators

Abstract: A new technique for suppressing the stimulated Brillouin scattering (SBS) using isolator(s) is proposed; the performance of suppression and the optimal positions of isolators are discussed. In a preliminary experiment using one isolator, the threshold power increased by 1.2 dB

All-optical FM mode-locking of fibre laser

Abstract: A novel method of all-optical active mode locking which relies on the nonlinear process of crossphase modulation is described. Mode locking is achieved by using a stream of optical pulses propagating along a length of optical fibre to provide a periodic phase perturbation of the laser cavity. The technique is demonstrated using an erbium-doped fibre ring laser.

Fast optical packet switching based on WDM

Abstract: An optical switch capable of routing a 3-Gb/s bit stream in 10-ns packets between ten different destinations is demonstrated. Switching time between destinations is 2 ns. The switch is based on wavelength division multiplexing (WDM) technology. It uses a fast tunable laser capable of addressing 24 discrete optical frequencies spaced by 40 GHz. >

A terminal for a frequency divided, optical communication system

Abstract: An optical terminal has optical waveguides, 3-dB couplers, laser diodes, laser diodes provided with gratings, and connections on a substrate made of semiconductor material. The grating laser diodes have an external cavity which is formed by the waveguides and delimited by mirrors. Each of the laser diodes has a respective electrical connection through which the diodes can be switched between a light-absorbing mode, a light-amplifying mode, and a light-emitting mode, with the aid of electric current signals, and the diodes are also able to detect a light signal. The terminal can perform a number of functions. A light signal can be received, detected, amplified, and further transmitted. A narrow band light signal of desired wavelength can be generated within a broad wavelength area through the grating diodes in the cavity, and amplified and further transmitted. A light signal received having a plurality of wavelengths can amplify and detect a selected one of the wavelengths through the laser diodes in the cavity. Coherent reception of a light signal can be performed and a phase-modulated light signal can be transmitted.

Technique for translating light-wave frequency by using an optical ring circuit containing a frequency shifter

Abstract: A new technique for the external frequency translation of light waves is proposed. The technique enables the stepwise sweeping of an optical frequency in time over a wide range. The frequency translator is composed of an optical pulse modulator and an optical ring circuit that contains an acousto-optic frequency shifter and an optical amplifier. The pulse launched into the ring circuit undergoes a frequency shift for each complete trip around the ring circuit, and the frequency is translated considerably from the original input pulse. We confirm a frequency translation of as much as 8 GHz for a 1.5-μm light wave, in which the sweeping is strictly linear with respect to time.

Method and apparatus for communicating amplitude modulated signals over an optical communication path

Abstract: A block of amplitude modulated television channel signals frequency modulates an optical communication path. In one embodiment, the AM modulated channel signals FM modulate an RF subcarrier which, in turn, is used to intensity modulate an optical carrier for transmission. Frequency modulation of the RF subcarrier by the amplitude modulated channel signals is advantageously performed at microwave frequencies. The FM modulated subcarrier signal is then converted down to a frequency range compatible with transmitter and receiver components used in the system. The frequency modulation and conversion can be performed by a pair of voltage controlled oscillators coupled in a push-pull mode of operation. The outputs of the oscillators are combined in a double balanced mixer to down convert the FM signal spectrum. In another embodiment, the optical frequency of an optical carrier is FM modulated by the block of AM signals. Receivers for the FM modulated band of AM channel signals are also disclosed.

Optical communication link with correction of non-linear effects and optical signal processing method

Abstract: An optical communication link with correction of non-linear effects comprises an optical fiber transmission line subject to chromatic dispersion and non-linear effects and correction means for limiting the disadvantageous consequences of this dispersion and/or these non-linear effects. The correction means comprise at the output of the transmission line a dispersion compensator adapted to apply dispersion in the opposite direction to and of lower absolute value than the dispersion due to the transmission line.